Self-synchronized saw-tooth generator



pr l, 1947. I W. 1 POCH 2,418,425

sELF-sYNcHRoNIAzED SAW-TOOTH GENERATOR Filed Jan. 27, 1943 I EFLECNGmhwrefloc `TTOIPIVEK Patented Apr. 1, 1947 SELF- SYNCHRONIZED SAW-TOOTHGENERATOR Waldemar J. Poch, Morristown, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application January27, 1943, Serial No. 473,666

(Cl. Z50-36) 2 Claims.

This invention relates to television or oscillographic apparatus, and isparticularly concerned with the circuits thereof serving to supplyenergy to the deecting coils or plates of a cathode ray tube to deflectthe electron beam therein developed across an impacted target area.

Broadly speaking, the invention is concerned primarily with televisionreceiving or transmitting apparatus wherein a cathode ray tube is usedeither as an image scanning or an image reproducing tube, although theinvention also finds application tothe usual oscillograph type ofapparatus wherein a transient or other phenomena produced on the viewingtarget by a cathode ray tube is caused to appear atpredetermined'repetition rates.

In its essence, the invention herein to be disclosed includes the use ofa triggering and discharge tube in co-operative relationship withrespect to an energy storing element and arranged to co-operate with asuitable output tube which delivers energy to the electron beamdelecting system.

In combination with this arrangement, provision is made for feedingbacka portion of the energy from the output tube to the discharge tube tocontrol its operation. Provision is also made fOr exercising an externalcontrol over the rate at which the discharge .tube is controlled by theenergy feedback from the output tube by means of a synchronizing impulseserving as an auxiliary control to lock definitely the operational cycleto some desired value.

In its essence, the invention herein provided is for the purpose ofsimplifying previously known circuits and, at the same time, avoidingthe use of the frequently used so-called blocking oscillator tubenormally used to develop energy pulses to control the discharge actionof the discharge tube whereby the desired form of sawtooth wave energyis developed.

A still further object of this 'invention is that of providing a circuitand system which operates efficiently and yet avoids the necessity ofheretofore used oscillator tubes incorporating both tube elements,transformers and the like, so that the present invention not only makesprovision for reducing the number of tubes heretofore used and requiredfor deflection purpose-s, but also is of a nature such that the weightof the component parts of the system is reduced by virtue of thecomplete omission of heretofore used transformers embodying heavy ironcores or the like.

Other objects and advantages of the invention are those of providingsimplifications in circuit arrangements which overcome known defects ofprior art systems and which, at the same time, serve to provide improvedoperation of the ycomplete system.

Other objects and advantages will become apparent from reading thefollowing specification and claims in connection with the accompanyingdrawing, wherein one form of circuit capable of accomplishing the aimsand objects of the invention has been set forth by way of diagrammaticillustration.

Referring now to the drawing, the herein described deflecting circuitcomprises essentially two independent tube elements II and I3, in whichthe tube I I serves as the so-called discharge tube and the tube i3serves as the socalled output tube which is to deliver the energy to theelectron beam deecting system. l

In the arrangement disclosed, the discharge tube II comprisesessentially an envelope including a cathode I5, a control electrode I'Iand an anode or plate electrode I9, with the cathode I5 preferablyconnected to ground 2I in its normal form of operation, although it isapparent that the connection may be made to any other point ofsubstantially iixed potential.

Connected between the output or anode element I9 and ground 2| is astorage condenser 23 which is adapted to be charged from a source ofenergy (not shown) but connected to the terminal 25, marked +B (thusrepresenting also a source of plate potential) which charges thecondenser 23, preferably through the high resistor 21, so that when thecondenser is periodically discharged by conduction within the dischargetube I I, a sawtooth voltage wave, such as that represented at (a), willbe produced at the point 29, and represents the potential of the upperplate of the condenser 23 relative to ground 2l, for instance. In normaloperation, the sawtooth voltage wave (a) appearing at the point 29 isthen fed by way of the coupling condenser 3l to the control electrode 33of the output tube I3, which includes also the cathode 35, the screenelectrode 3l and the plate or anode output electrode 39,

with the cathode element 35 preferably biased terminal winding 45 of anoutputtransforiner 41.

The secondary winding 49 of the output transdetermined largely inaccordance with the fre? quency of the deflecting energy applied to thedeflecting coils,

It will be noted that the screen electrode 3l is also shown as derivingits potential relative to ground 2| by virtue of the connection of thesource of energy at the terminal 43. I-Iigh frequency energy isby-passed to ground 2l from the source connected to the terminal 43 byway of the condenser 53. Thus, voltage for both the screen electrode 3land the'plate or anode electrode 39 is supplied from the terminal ?,Aand flows through the transformer primary 45.

A connection` is provided between the terminal point 5-5 at the upperend of the transformer primary l5 back to the control 'electrode I'l ofthe vdischarge tube II through the conductor 5I in which is provided thecapacity element 59. At the same time, a leak resistor 6I is providedbetween the control electrode Il of the discharge tube I I and ground2l. v

In case of electrostatic deflection of a cathode ray beam, thetransformer 41 may be omitted and the energy output from tube I3 may befed to the electrostatic deflecting plates (not shown) and a suitableform of differentiating circuit is then included in the line 51 tosupply an energy pulse to control the operation of the discharge tube II, as will hereinafter become more apparent in considering the operationof the system.

Control impulses fromA any suitable source of synchronization pulses maybe applied to regulate the operation of the system from an externalsource by way 'of the connection provided at the terminal E3 by way ofthe conductor 55 to the control electrode Il. As an alternative, thesynchronizing control signal may be supplied through l of the blockingoscillator type is used. Such a tube operates generally to produceoscillations by virtue of a coupling connection provided between theoutput and the input circuit through a transformer with the feedbackenergy adapted to apply a charge to a grid condenser to drive the tubegrid positive. At such time, the grid potential becomes quite positivewith regard to the cathode of the tube, so that the tube commences t0draw grid current and, accordingly, a negative charge is placed on thegrid condenser which then tends to block the tube or bias the cutoff;The same potentials which are active upon the control elec,-v trode ofthe blocking oscillator tube are applied to the control electrode orgrid of the discharge tube, which would be equivalent to the tube IIherein disclosed. l However, in the circuit herein set forth, it will benoted that there is no blocking oscillator tube included in the system,but, to the contrary, the synchronizing signalinput energy which is inthe natureof apulse, it being assumed herein 4 that the synchronizingsignals for controlling the operation of the cathode ray device havebeen separated from video signals which they accompany, will be appliedto the input terminal 63. Let it be assumed, then, that the tube II iscaused to draw current at such a time.,

Prior to the time when the tube II draws current, the condenser 23 hasbeen charging through the resistor 2l, so that the upper plate of thelcondenser charges positively relative to ground along the path indicatedby the sawtooth wave form (a), but as soon as the tube II draws current,vthe charge in the condenser is discharged through the tube and a newcharge is built up to form the next cycle of the sawtooth wave form.

The voltage thus appearing at thev point 29 is then transferred throughthe coupling condenser 3l. tov control the grid of the output tube I3and to cause it to draw current, With the controlling voltage being ofthe form shown by the wavey (a) When the tube I3 draws current, itsoutput.V energy is fed through the transformer primary d., but by virtueof the effect of the transformer winding, there is produced not only asawtooth .i component, as represented by the wave (b), but

also an impulse component of oppositeipolarity, in this instancepositive as indicated by the tipv4 portions (c) of the wave (b), as wellas sawtooth component (d) herein indicated as being of neg--V atvepolarity. The impulse component-(c) is then fed back to the controlVelectrode I'l of the, discharge tube II through the condenser 5.9, so4that it will serve toV trigger the tube I I and cause it to draw currentto discharge the condenser 23, which has acquired a charge intermediate,the recordings of each of the impulse components (c) andl thus anothersav/tooth of energy is` applied to the control electrode 33 of theoutputtube.v

In the case of the transformer shown, the impulse section of the wave isavailable,y as well as the sawtooth section, but if only the sawtoothsection were developed, it is apparent that the impulse section couldvstill be made available byf feeding a part of the output of the outputstube I3 to condenser 5S through'any desiredl type of differentiatingcircuit.

Whatever charge is built up in the condenser 59 by virtue of thefeedback connection (both to cause tube Il to draw current and later toblock it) leaks olf within the time cycle measured by the time constantof the condenser 59 and theV leak resistor 6 I, either of which elementsmay be varied as desired to alter the time constant.

From what has been stated, therefore, it is apparent that the operationof the tubes Il and I3, taken together, provides a purely automaticmeans to provide for the generation of sawtooth wavel impulses which maybe transferred to the output terminals 5l to control the deecting'coils(not shown) for defiecting a cathode ray beam. The rate at which thesawtoo-th deflection takes placewill be determined, generally speaking,by the time constant introducedv through the condenser 59 and theresistor 6I. However, for the purpose of exercising an auxiliarycontrol,'it is apparentV that the receipt of synchronizing impulses atthe terminal B3 will be adequateto trigger the tube II, if the timeconstant of the condenser 59 and the resistor Bill is made; equal to, orjust veryl slightly longer, or even j ust slightly shorter (under someconditions)` than theV time interval be: tween thevreceipt of successiveimpulse. synchroy nizing signal energy at. the'input terminal, 6%

Thus, the synchronizing signals, as received, serve ergy, shown by curve(a), to cause the deflection to be completely synchronous with that ofthe control point, but, in the absence of receipt of synchronizingsignals, the circuit functions in purely automatic manner to maintainthe continual deflection of the cathode ray beam which is controlled bythe deflecting coils notI shown.

It is apparent, furthermore, that the charging energy to the condenser23 may be varied by varlation of the value of the resistor 21 so as tocontrol, for instance, either the height or the Width of the picture, inaccordance with the amplitude of the deflection produced, or thiscontrol may be exercised by virtue of a second resistor placed in serieswith the resistor 21.

Other and further modifications may Vbe resorted to Where suchmodifications fall Within the spirit and scope of what is hereinafterclaimed.

I claim, and desire to secure by Letters Patent, the following:

1. A sawtooth Wave generating circuit comprising an electrical storageelement having one terminal thereof connected to ground, a source ofenergy and a substantially constant current element connected to theungrounded terminal of said storage element normally to charge itrelatively slowly in the direction of maximum charge, a first thermionicmeans having an anode, a cathode, and a control electrode, a directconnection from the cathode to ground and a connection from the anode tothe ungrounded terminal of said storage element to reduce the chargeabruptly substantially to a minimum value during conductive periods ofthe said thermionic means, a

second thermionic means connected to said energy storage element toproduce amplified output energy of a Wave form closely approximatingthat of the electrical charge in said storage element, a differentiatingmeans for developing energy pulses from the amplified output energy attime periods corresponding to the abrupt change in storage elementcharge, a time constant circult including a series connected capacityand a resistor element for supplying said developed energy pulses to thefirst thermionic means to control the operative periods thereof, saidtime constant period being of the same order as thatv desired in thedeveloped saWtooth Wave, and a utilization circuit connected to respondto the output energy of the second thermionic means.

2. The wave generating circuit claimed in claim l comprising, inaddition, means for supplying auxiliary control signals of predeterminedfrequency to said rst thermionic means whereby the frequency of thedeveloped sawtooth substantially coincides with that of the controlsignals.

WALDEMAR J. POCI-I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,159,493 Wright May 23, 19392,241,619 Sherman May 13, 1941 2,300,524 Roberts Nov. 3, 1942 2,254,031Faudell Aug. 26, 1941

